In organic electroluminescence (hereinafter referred to as organic EL) elements, a charge transporting thin film including an organic compound is used as a light emitting layer or a charge injection layer. Particularly, a hole injection layer serves for transfer of electric charges between an anode and a hole transport layer or a light emitting layer, thereby fulfilling an important function for achieving low-voltage driving and high luminance in the organic EL element.
Methods for forming a hole injection layer are generally classified into dry process represented by the vapor deposition method and wet process represented by the spin coating method. When these processes are compared, the wet process permits more efficient production of thin films with high flatness over a wider area. Under the present trend toward organic EL displays of larger areas, therefore, there is a demand for a hole injection layer that can be formed by a wet process.
In consideration of the above-mentioned circumstances, the present inventors have developed charge transporting materials which are applicable to various wet processes and which give thin films capable of realizing excellent EL element characteristics when applied to the hole injection layer in organic EL elements, and compounds which are to be used for the charge transporting materials and show good solubility in organic solvents (see, for example, Patent Documents 1 to 4).